Industrial machinery and processes generate tremendous amounts of heat which must be continuously absorbed by another medium such as water or air if these machines and processes are to continue to operate efficiently. Typically the heat generated by industrial machinery or processes is absorbed by water which passes through a heat exchanger, such as metal coils. The heated water is then discharged while a continuous source of cool water is supplied to the process (once through cooling). In `closed` cooling systems, the heated water is circulated to a cooling system, typically an atmospheric cooling tower, to reduce the water temperature before recycling the cooled water back to the heat producing process.
Although cooling towers are used in many industrial processes, power generating plants are of particular interest because of the magnitude of the heat produced and effect of cooling water on process efficiency. These plants are typically powered by steam which is generated to turn turbines. Turbines operate by passing expanding steam through a series of nozzles which are designed to convert the energy of expansion directly into rotational motion. The rotational motion causes an electromagnetic generator to generate electricity on a commercial scale. The steam generated to turn the turbine may be generated by the combustion of fossil fuels or nuclear power. The turbine exit steam generated must be cooled and condensed to water which is recycled to generate more steam. The condensation process occurs in a condensing heat exchanger where heat from the steam is transferred to cooler circulating water. The now heated circulating water is pumped to a cooling tower to be cooled and then recycled back to the condensing heat exchanger.
The water to be cooled in the cooling tower is circulated and distributed in direct contact with cooler air which is circulated by mechanical fans or natural convection. Air flow may be across the cascading liquid or counter current.
Typically, the cooling tower consists of an enclosure which contains a hot water distribution system, a set of louvers or baffles (fill) for breaking the water into small films and droplets, and a cooled water collection basin. There are several internal gridwork arrangements, all designed to enhance water splashing and film formation.
There are many types of manufactured cooling towers including mechanically induced and naturally induced draft towers, crossflow and counterflow towers, wet/dry plume abatement towers, and water conservation towers.
It is known to use certain surfactants in cooling towers to achieve certain results. For instance anionic surfactants are used for cleaning and emulsifying, cationics are used as biocides, and nonionics are used as defoamers for biocides. Although surfactants are used for such purposes in cooling towers, the literature suggests that the use of surfactants in cooling towers has adverse effects. For instance, water can easily become contaminated by surfactants. As a result, surfactants generally reduce the liquid and gas side heat transfer coefficient, and can cause deterioration of the performance of cooling towers. Experimental data suggest that a reduction in heat transfer can also occur. See Dabiri, A. E., et al., "Influence of Generic Chemical Additives on Cooling System Performance", Electric Power Research institute Final Report: CS-5903, July (1988).